Sir David Nicholson, the first chief executive of the new NHS England, has resigned and there are nine months in which to find a replacement.

No one really knows what the job will be. But we do know that the NHS is in turmoil. Alongside the most complex reorganisation in its history, inquiries into poor care, allegations of cover-ups and bullying, bitter battles over service reconfiguration, and an unprecedented level of scrutiny, the pressures on the service are immense.

It is no exaggeration to say that the NHS will soon be crippled unless we acknowledge that the way in which we provide healthcare is neither safe nor sustainable. Nothing short of a complete transformation needs to happen in a political and bureaucratic environment that is hugely resistant to controversial change.

Whoever is appointed to the top job must have a clear vision of how this new body will deal with the challenges, but without many of the traditional levers of authority. He or she will not be the "boss" of the NHS, although many will presume that they are. Indeed, there is no single person in charge of the reformed NHS.

Being able to describe the role clearly and simply, whether that be to the public, patients, staff or politicians, will be essential, as will the strength to hold on to that clarity when things go wrong and everyone wants to know who is in charge.

The key attribute will be credibility in the eyes of a wide spectrum of people, from patients to politicians, consultants to chief executives. Independence from politicians is important, but unless this individual can gain the confidence of ministers, professional organisations and patients, they are likely to crash before takeoff. Empathy with vulnerable people is essential, as are the traditional management skills, but, beyond this, a willingness to communicate with people in a human and yet authoritative manner is vital.

Given recent events, the successful candidate must expect a level of personal scrutiny far beyond the norm for public servants. So it will be important to be able to face this with confidence. There is no way that someone who works in isolation or believes they sit at the top of a hierarchy will succeed in this job. Teams and clinical networks across the NHS will need to be built and rebuilt. This is hard because it requires the forging of partnerships based on a deep understanding of complementary strengths and weaknesses and respective priorities. It cannot be "directed" and anyone who has an ego of their own to burnish need not apply.

Professional background is far less important than whether the person can embody these qualities.

Could someone from outside the NHS, or even the UK, be successful? This is difficult to say. Our track record of helping people to enter the NHS at senior levels is poor. The honeymoon period is likely to last only until something goes wrong – possibly days or weeks. There will be little opportunity for a carefully paced induction programme, so it needs to be someone who has an understanding of the NHS.

As a former NHS CEO there are two reasons why I don't want this job. First, I think it is time for a generational change at the top, and I am firmly part of the current generation. Second, I have experienced nine NHS reorganisations in my career, of which five have involved leading the destruction of my own organisations, and I simply cannot face that again with enthusiasm. I shall watch the race with interest. It is an important appointment for me and my family, and for you and yours.